Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019
ASSETS
Real estate and development in process, net		$ 17,518,173	$ 17,622,212
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,919,157	2,922,408
Other Liabilities		366,852	387,994
Total liabilities and equity / capital		21,829,698	21,284,905
Carying value of the Company's investment in unconsolidated joint ventures		1,377,338	955,647
Right-of-use assets - finance leases		237,394	237,394
Right of use assets - operating leases		148,057	148,640
Lease liabilities - finance leases		227,067	224,042
Lease liabilities - operating leases		200,573	200,180
Unconsolidated Joint Ventures [Member]
ASSETS
Real estate and development in process, net	[1]	4,469,460	3,904,400
Other assets		578,468	502,706
Total assets		5,047,928	4,407,106
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,312,938	2,218,853
Other Liabilities	[2]	638,892	749,675
Members'/Partners' equity		2,096,098	1,438,578
Total liabilities and equity / capital		5,047,928	4,407,106
Company's share of equity		956,136	591,905
Basis differentials	[3]	398,976	341,318
Carying value of the Company's investment in unconsolidated joint ventures	[4]	1,355,112	933,223
Right-of-use assets - finance leases		248,900	383,900
Right of use assets - operating leases		11,900	12,100
Lease liabilities - finance leases		391,000	510,800
Lease liabilities - operating leases		17,400	17,300
Colorado Center [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		310,100	311,300
Unconsolidated Joint Ventures [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Other Liabilities		22,200	$ 22,400
Gateway Commons Complex [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		55,700
Carying value of the Company's investment in unconsolidated joint ventures	[5]	$ 348,143

[1] At March 31, 2020 and December 31, 2019, this amount includes right of use assets - finance leases totaling approximately $248.9 million and $383.9 million, respectively, and right of use assets - operating leases totaling approximately $11.9 million and $12.1 million, respectively.

[2] At March 31, 2020 and December 31, 2019, this amount includes lease liabilities - finance leases totaling approximately $391.0 million and $510.8 million, respectively, and lease liabilities - operating leases totaling approximately $17.4 million and $17.3 million, respectively.

[3] This amount represents the aggregate difference between the Company’s historical cost basis and the basis reflected at the joint venture level, which is typically amortized over the life of the related assets and liabilities. Basis differentials result from impairments of investments, acquisitions through joint ventures with no change in control and upon the transfer of assets that were previously owned by the Company into a joint venture. In addition, certain acquisition, transaction and other costs may not be reflected in the net assets at the joint venture level. At March 31, 2020 and December 31, 2019, there was an aggregate basis differential of approximately $310.1 million and $311.3 million, respectively, between the carrying value of the Company’s investment in the joint venture that owns Colorado Center and the joint venture’s basis in the assets and liabilities. At March 31, 2020, there was an aggregate basis differential of approximately $55.7 million between the carrying value of the Company’s investment in the joint venture that owns Gateway Commons and the joint venture’s basis in the assets and liabilities. These basis differentials (excluding land) shall be amortized over the remaining lives of the related assets and liabilities.

[4] Investments with deficit balances aggregating approximately $22.2 million and $22.4 million at March 31, 2020 and December 31, 2019, respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.

[5] Investments with deficit balances aggregating approximately $22.2 million and $22.4 million at March 31, 2020 and December 31, 2019, respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets.